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The softest thing overcomes the hardest thing in the universe. ...Lao Tzu (570-490 BC)
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Author Topic: Regarding pin-hole images.  (Read 1488 times)
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RUMI
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on: November 22, 2012, 10:43:37 pm » posted from:Jodhpur,Rajasthan,India

Reference:  http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=38.0


Sir, i was very much delighted to find your website on the net while searching for pin hole images.
Actually i was trying to find solution to a different phenomenon .
" Take a mirror outdoors when sun is in the sky.Observe the reflection of the sun onto a wall. If the wall is nearby we see the shape of the mirror and if the wall is far away we see the shape of sun."

I realise that this is similar to a pin-hole image, execpt that the image is on the opposite side.Because a mirror is equivalent to a hole, both differing only in the side where image is formed.

I would be happy if the java applet is made so as to vary the distance of the image plane from pin-hole and also if along with the letter 'F', there is also object like sun(a round ball).

Eagerly waiting for your response...Thank you.
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RUMI
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Reply #1 on: December 08, 2012, 04:57:52 pm » posted from:Jodhpur,Rajasthan,India

I have worked out to realise that a pin-hole phenomenon is similar to dilation of two images on the image plane.
* one image is that of the hole shape, with dimensions proportional to the actual size.
*Other image is that of the object from which light reaches the pin hole.(Ex: sun , in case of a mirror reflection)

What actually happens is , the modified image of the hole on image plane is nearly equal to that of the actual size of hole.(because , distance from hole to image plane is negligible with respect to distance from light source to pin hole)
  where as a similar fraction of the big size of light source(ex sun in our case),gives a size very  much smaller (negligible w.r.t sun ), yet bigger than that of the modified pin hole.
  Thus the dilation of these two images gives the image of sun.


To make this clear to those who don't know what dilation means:
  consider you have a big circle and a small rectangle(or any other shape).What you have to do is, trace the area covered by the circle making the center of circle pass through every point on the rectangle.So, if the rectangle is very small, it is as if the center of circle has not moved(nearly), thus the trace again gives a circle.

If the image plane is very near to the pin hole(mirror in our case), the shape of modified pin hole dominates the shape of the (circle)sun. i.e, you have a small circle and a big rectangle.Now if similar process as mentioned above is done, it looks as if the image of rectangle is not disturbed , except blurring at he edges.
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ivwiwba
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Reply #2 on: January 19, 2013, 10:10:32 am » posted from:FUQING,FUJIAN,CHINA

I just required some information and was searching on Google for it. I visited each page that came on first page and didn’t got any relevant result then I thought to check out the second one and got your blog. This is what I wanted!-*-
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